Pedestrian and Bicyclist Intersection Safety Indices

User Guide

CHAPTER 5. Q & A ON MODEL APPLICATION

Q: Is there a specific safety index value at which safety improvements would be recommended at a site?

A: No, the purpose of this tool is not to dictate specific safety index values to serve as "warrants" for safety treatments. Rather, the purpose is to assign safety index values to crossings and bicycle approaches with the goal of providing the practitioner with the means to prioritize these sites for the purpose of further safety evaluation. For example, a practitioner may have 30 crossings in his or her jurisdiction to evaluate with respect to pedestrian safety. The practitioner would use Ped ISI to assign safety index values to each of the 30 crossings. The crossings with the highest values would be the first crossings where the practitioner should conduct indepth evaluations to determine if pedestrian safety problems exist at those sites. Such an evaluation may include an investigation into the crash history of the site, which may lead to countermeasure recommendations from other resources such as PEDSAFE. Other evaluations may include pedestrian counts and behavior studies or pedestrian conflict analysis.

Q: Can the Ped ISI or Bike ISI values from each leg be combined to produce a safety index value for the whole intersection?

A: If the user wishes to produce a safety index value for an entire intersection, the suggested method is to average the index values from all legs. However, caution should be used in this approach. Some intersections may have one leg that is high priority for safety evaluation (high index value) and three legs that are low priority (low index values). If the leg safety index values are averaged at this intersection, the result will be a low intersection safety index, and the high priority of the one leg may go unnoticed.

Q: Do all three Bike ISI values (through, right, and left) need to be calculated each time?

A: If bicyclist traffic is expected to perform all three maneuvers at the intersection, it is advisable to evaluate the safety of all maneuvers—through, right, and left.

Q: Are Ped ISI and Bike ISI to be used only at four-leg intersections or can they be used for intersections with three, five, and six legs?

A: Ped ISI and Bike ISI were developed using three-leg and four-leg intersections. Since the models produce safety index values for individual legs instead of an entire intersection, it is possible to use Ped ISI and Bike ISI at intersections with five and six legs. Many of the factors that affect pedestrian or bicyclist safety at four-legged intersections would affect safety similarly at five-leg or six-leg intersections. However, safety index values produced for five-leg or six-leg intersections should be used only with the understanding that the models were not developed using intersections of that type.

Q: Can Ped ISI and Bike ISI be used to prioritize midblock crossings?

A: No, Ped ISI and Bike ISI were developed for intersections only.

Q: Can Ped ISI and Bike ISI be used to prioritize legs of a roundabout?

A: No, Ped ISI and Bike ISI were developed for signalized or stop-controlled intersections only.